Field of the Invention
The present invention relates to a method of producing aliphatic and cycloaliphatic diols by catalytic hydrogenation of dicarboxylic acid esters.
Discussion of the Background
Cycloaliphatic and aliphatic .alpha.,.omega.-diols may be manufactured by the hydrogenation of the corresponding dicarboxylic acid esters. As catalysts for the hydrogenation, copper catalysts are preferably used, possibly with chromium and barium as promoters, and with or without a support. Other promoters which may be used include the alkaline earth metal, Ba, and alkali metals, such as Na and K. However, hydrogenation carried out with these catalysts, either in a liquid bath or in a trickling liquid, is not capable of achieving high selectivity for the desired diol, if high conversions are to be attained. Therefore, it is necessary to refine the crude product from the hydrogenation by distillation, in order to separate the components which boil at higher temperatures than the diols.
Thus, in European Patent 55 the production and use of a hydrogenation catalyst are described, in which aqueous solutions of salts of copper, nickel, and/or cobalt are mixed with alkali silicate solutions in a specified ratio, with the metal content of copper, nickel, and/or cobalt in the finished catalyst being 40-80 wt. %. In Example 1 of European Patent 55, diols are produced by hydrogenation using a copper catalyst over silica suspended in the amount of 5 wt. % in a mixture of the corresponding C.sub.4 -C.sub.6 -dicarboxylic acid methyl esters, at a mean temperature, T.sub.mean, of 230.degree. C. and a pressure of 250 bar. After a reaction time of 12 hr, the original ester number of 700 fell only to 60.
DE-PS 2,611,374, discloses catalysts for the hydrogenation of carboxylic acid esters to form the corresponding alcohols, which are comprised of copper, chromium, and alkali compounds, and possibly an alkaline earth metal and a support. It is specified that 0.3-0.7 g-atom of chromium per g-atom of copper must be used. Thus, for hydrogenation of an adipic acid hexanediol ester, dissolved 1:3 in 1,6-hexanediol, a Cu-CrNa catalyst is used, in a hydrogenation reactor at a T.sub.mean of 200.degree. C. and a pressure of 250 bar, with a catalyst loading of 0.4 kg of mixture per liter of reaction space per hr, and a hydrogen throughput of 50 liter (STP) per liter of reaction space per hr, which results in practically complete conversion. However, on the basis of the dicarboxylic acid converted, the yield of 1,6-hexanediol is only 98.5-99%, with a distillation residue of 0.5-1%.
According to DE-PS 1,154,448, high molecular weight alcohols can be produced by catalytic hydrogenation of fatty acid esters by copper multialloy catalysts. For example, according to Example 3 of DE-PS 1,154,448, adipic acid di-n-butyl ester was hydrogenated to 1,6-hexanediol on a CuZnCr catalyst, with no carrier, at a T.sub.mean of 250.degree. C. and a pressure of 220 bar, with a catalyst loading of 0.27 kg ester/liter/hr and a gas loading of 10,570 liter (STP) per liter catalyst per hr. With nearly complete conversion (ester number less than 3), after distillation a yield of 90-95% was obtained. Sebacic acid di-n-butyl ester was hydrogenated to 1,10-decanediol under the same conditions, with a yield of 90-95% of theoretical.
According to DE-PS 1,159,925, a copper/chromium/potassium hydrogenation catalyst on a silicic acid support is described, wherewith the silicic acid, of a wide pore type with a specified active surface, is impregnated with the appropriate compounds and is dried. The finished catalyst contains 18-30 wt. % copper, 0.3-3.5 wt. % chromium, and 0.5-9 wt. % potassium.
According to Example 1 of DE-PS 1,159,925, at a T.sub.mean of 215.degree.-222.degree. C., a pressure of 200 bar, a catalyst loading of 0.1 kg adipic acid di-ethylhexyl ester per liter catalyst per hr, and a gas loading of 282 liter hydrogen (STP) per liter catalyst per hr, with a CuCrK catalyst on a silica support, 1,6-hexanediol was obtained following distillation with nearly complete conversion (ester number=2) and a yield of 94.5% of theoretical. Hydrogenation of sebacic acid di-n-butyl ester (Example 1f) at a T.sub.mean of 220.degree.-225.degree. C., with the other conditions being the same, gave 1,10-decanediol following distillation with nearly complete conversion (ester number=3) and a yield of 96% of theoretical. Hydrogenation of hexahydroterephthalic acid di-n-butyl ester (Example 1d) at a T.sub.mean of 210.degree. C. and a gas loading of 28.2 liter hydrogen (STP) per liter catalyst per hr, with the other conditions being the same, gave 1,4 -di-hydroxymethylcyclohexane following distillation with nearly complete conversion (ester number=1) and a yield of 95% of theoretical.
DE-PS 1,202,269 discloses the production of 1,4-di-hydroxymethylcyclohexane by catalytic hydrogenation of a terephthalic acid dialkyl ester to a hexahydroterephthalic acid dialkyl ester (first stage), on a palladium catalyst, and further hydrogenation to form the product (second stage), on a copper chromite catalyst. Suitable catalysts contain copper (CuO basis) in the amount of 30-80 wt. %, chromium (Cr.sub.2 O.sub.3 basis) in the amount of 15-55 wt. %, and barium (BaO basis) in the amount of 0-15 wt. %.
In the Examples of DE-PS 1,202,269, the hydrogenation of hexahydroterephthalic acid dimethyl ester is described in which a catalyst comprised of copper chromite and a support is used which has the following composition:
Cu 33.2 wt. % (as CuO); Cr 38.0 wt. % (as Cr.sub.2 O.sub.3);
Ba 10.4 wt. % (as BaO); Na 3.5 wt. % (as Na.sub.2 O); and SiO.sub.2 9.5 wt. %.
For the ester hydrogenation at a T.sub.mean of 260.degree.-270.degree. C. and a pressure of ca. 380-390 bar, a conversion of 97% was reported, with the liquid reaction product mixture being 68 wt. % 1,4-dihydroxymethylcyclohexane. Correspondingly, for the hydrogenation of hexahydroterephthalic acid dibutyl ester carried out under the same conditions, practically complete conversion was reported, with the liquid reaction product mixture being 49.1 wt. % 1,4-dimethylcyclohexane. Since no data are given on the amounts of the gaseous carbon compounds formed, the maximum yield for the methyl ester is 94.4% of theoretical, and for the butyl ester, 96.8% of theoretical. The catalyst employed loses its activity after 2 months of service, due to the severe reaction conditions.
Thus, all of the known methods of catalytic hydrogenation of dicarboxylic acid esters to form diols exhibit drawbacks, such as the requirement of relatively severe reaction conditions, the loss of catalyst activity after relatively short operating times, and the need for refining by distillation because of the formation of high-boiling by-products (DE-PS 2,611,376).